A water heater or the like for household use is provided with an apparatus that detects carbon monoxide generated when incomplete combustion occurs and notifies the risk thereof at an early stage. Such a gas component considerably affects a human body. According to the guidelines from LP gas safety committee, it is set that a carbon monoxide concentration of approximately 200 ppm (parts per million) causes headaches. Although various methods have been known as a method of detecting a gas component having a relatively higher concentration, the detection methods have been limited for detecting the gas component having a concentration of ppb (parts per billion) to ppt (parts per trillion), which corresponds to an extremely low concentration.
At a disaster site or a site at which an act of terrorism occurs or the like, it has been desired to sense the risk in advance by detecting an extremely small amount of the gas component. The gas component having an extremely low concentration is often detected by use of large equipment in research facilities. In this case, a large sized installation type apparatus, which is expensive and has large weight and volume, such as a gas chromatography or mass spectrometer is required. The case when direct measurement is desired on the go relies on a simple measurement method that detects the gas component by use of a biological reaction mechanism, but has many problems of a storage life, temperature management, a limit of determination whether the gas component is present or not, and the like. Under such circumstances, an apparatus has been required that is capable of detecting the gas component having an extremely low concentration in real time, in other words, an apparatus that has a smaller weight and volume and a better portability and enables selective and higher sensitive detection of the gas component having an extremely low concentration in the order of ppt to ppb.
As a detection element for the gas component having a low concentration, for example, an element has been known that has a conductive layer in which a surface of a carbon nanostructure is surface modified with a substance that selectively reacts with or adsorbs a specific substance and measures a potential difference or the like that changes depending on the gas component that has adhered to the surface of the carbon nanostructure. In such a detection element, there is a possibility that it is impossible to accurately detect a detection target gas component when a component or the like similar to the detection target gas component is mixed in the gas obtained from, for example, the air as impurities. Besides, the detection substances are limited to alcohol, nitrogen oxide, and so on whose molecular structure is simple and lack in complexity. There is known a detection element including a field effect transistor using a graphene film and a functional group provided on the graphene film as an element which detects material species in a solution. This detection element uses a single chain, an antigen, an enzyme, and so on forming a double spiral structure of DNA, and it aims at identifying biological species such as DNA in the solution.